Method and apparatus for producing mixtures of coke and mineral materials



Nov. 3, 1953 c. J. M FARLIN METHOD AND APPARATUS FOR PRODUCING MIXTURES OF COKE AND MINERAL MATERIALS Filed May 5, 1948 INVENTOR (Pin-lens Ll/4J2??? WWW ATTORNEYS uo mo. .m 2.. mwmz zu Q, I ozjkkmm .530 MM W WQ/NZ H 200 29252302 um hw a x/ a oziou mo w zou A L M2: $55 a Q Q 68 zumum x 200 Q Elmo: I200,

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Patented Nov. 3, 1953 METHOD AND APPARATUS FOR PRODUCING MIXTURES F COKE AND MINERAL MA- TERIALS Charles J. McFarlin, Darien, Conm, assignor to Air Reduction Company, Incorporated,- New York, N. Y.', a corporation of New York Application May 5, 1948 Serial No. 25,113

7 Claims.

This invention relates to a method and apparatus for producing mixtures of carbonaceous fuel with mineral materials in preparation for subsequent treatment in furnaces.

There are numerous metallurgical and similar operations in which combinations of carbonaceous fuel with other materials are subjected to smelting and similar furnacing procedure. Heretofore, it has been necessary to produce coke in coke ovens, transport it to the situs of operation, and there mix it with other ingredients of the furnace charge. This entails considerable losses with respect to the valuable constituents of the coal, and transportation charges which add to the cost of the final operation. Thus, for example, in the manufacture of calcium carbide, coke is produced in a byproduct oven, often at a point remote from the carbide plant. The coke is transported to and mixed with lime at the .carbide plant. Similar instances in the metallurgical field involvingmixtures of ore and carbonaceous fuel are matters of common knowledge.

t is the object of the present invention to provide a simple and economical method of effecting the calcination of material such as limestone or ores and carbonaceous fuel in admixture therewith in a single continuous operation, thereby producing the desired mixture or agglomerate and utilizing the gases separated from the coal to supply heat for the operation.

Another object of the invention is the provision of apparatus suitable for the practice of the improved method.

Other objects and advantages of the invention will be apparent as it is better understood by l,

reference to the following specification and the accompanying drawing, which illustrates more or less diagrammatically a kiln with appurtenances to adapt it for the practice of the invention.

The invention will be described more particularly with reference to the production of mixtures of lime and coke suitable as a charge for an electric furnace in which calcium carbide is produced. As heretofore indicated, it has been the practice to burn limestone in a kiln to produce lime, produce coke, usually in a byproduct coke oven at some distant point, transport the coke to the site of the carbide plant and there mix the materials to provide the charge for the carbide In accordance with the present invention, a single kiln is employed. Limestone is fed continuously at one end of the kiln which is of the horizontal revolving type. Inpassing through the kiln, the limestone is subjected to sufiicient heat to drive off the carbon dioxide and produce lime. At the lower or discharge end of the kiln, coal is introduced at a point from 1 to 3 diameters from the end and thereby mixed with the lime as it advances. Any suitable coal of the coking or non-coking type may be employed, and it is subjected to sufficient heat in the kiln to drive off the volatiles and to produce a mixture of carbonaceous fuel with lime. The gases which are separated from the coal are burned by the introduction of air to a point adjacent that at which the coal is fed, thus producing a flame and the heat required for the operation by combustion of the volatile product of the coal. The mixture of lime and carbonaceous fuel or an agglomerate thereof is discharged from the end of the kiln to suitable cooling facilities from which it may be withdrawn for storage and use as a charge in the carbide furnace.

From this outline of the procedure, it will be apparent that the method is applicable, not only to the production of mixtures of carbonaceous fuel and lime, but also to mixtures of carbonaceous fuel and ores or other metallurgical materials where it is desirable to provide a mixture of carbonaceous fuel with the material in order to afford a charge for any furnace or similar heat-treating operation.

Referring to the drawing, 5 indicates a rotary kiln, the structure of which may be similar to that of apparatus of corresponding type which is commonly used in many industries. Thus, the kiln 5 will be mounted on rollers 6 and may be driven by any suitable means (not shown). The kiln is preferably slightly tilted so as to facilitate the movement of material therethrough. It may be provided with dams I or other means well known in the art to facilitate the mixing of the material as it flows through the kiln. Such means are not essential.

Atthe charging end, a hopper 8 is provided, through which the material, for example limestone, may be introduced continually by a weigh feeder 9. As the limestone advances through the kiln, it is subjected to a sufliciently high temperature to drive off carbon dioxide and thus produce lime.

At the lower or discharge end of the kiln, it is closed by a housing in having an outlet H through which the finished material is discharged for cooling and storage by a screw conveyor l2. A pipe I3 extends through the housing 9 to a point equal to from 1 to 3 diameters of the kiln from the end thereof. A screw conveyor M or other suitable conveying means is disposed in the tube and adapted to introduce coal from a supply hopper l5. A weigh feeder I6 delivers the coal to the hopper. Thus, the coal is delivered to a point within the kiln where it is mixed with the advancing lime and the mixture continues to advance through the kiln, being subjected to a sufiicient temperature therein to drive off the volatile content of the coal.

Air is introduced through a pipe I! to a point just beyond the end of the pipe I3. The air mingles with the volatile product from the coal and, being ignited, forms a flame which produces the heat necessary for the operation. The heated combustion products pass upwardly through the kiln to a dust chamber 18 and outlet flue it. Thus, it will be seen that combustion of the volatile products from the coal affords the heat necessary to complete the calcining of the lime.

The heat necessary to drive volatile products from the coal is obtained from three sources, sensible heat in the hot lime from the calcining zone, radiation from the main burner flame and the kiln walls in the hot part of the calcining zone, and from partial combustion of the volatile products from the coal. Air for the partial combustion can be admitted through a pipe 20. The amount of such combustion required is dependent upon the degree of heating of the coal which is desired, but in any case is so limited and controlled as to prevent the formation of carbon dioxide with the resulting consumption of fixed carbon and recarbonation of the lime.

It is to be understood that the usual devices for controlling kiln conditions in the various zones, such as the use of variable diameters, dams or baflies, may be used. The specific conditions required to be maintained in the coal heating zone are dependent upon the raw materials used. For example, if pebble lime of relatively large size is being made, agglomeration into larger particles is undesirable, so that conditions of heat and agitation should be controlled to avoid it. On the other hand, if reclaimed calcium hydrate sludge is being burned to produce a finely divided quick lime, agglomeration into larger par ticles is desirable. The sludge may be fed to the furnace in finely divided form or it may be previously briquetted or formed into pellets. Depth of the coal heating bed, speed of rotation, use and location of doctor knives or other scraping or agitating devices, rate of heating and choice of coal on the basis of agglutinating power, are all variables which may be used to control these conditions. Application of the method is not limited to production of a charge in exact furnace ratio of carbonaceous fuel to ore. Composition may be varied within wide limits to satisfy special requirements of over-all plant energy and material balance.

The heat required to accomplish coking is entirely a matter of the heat balance which is dependent upon the materials and purpose to which the process is applied. To make this point clearer, we will consider the following qualitative outline of the heat balance around the coking zone.

Heat in 1. Sensible heat in hot, burnt lime from the calcining zone.

2. Radiation from the main burner flame and the kiln walls in the hot part of the calcining zone.

3. Exothermic heat of the coking reaction. This quantity varies considerably with different coals and is of such magnitude as to be considered generally negligible.

4. From a partial combustion of gas in the coking zone of the kiln. This is accomplished, when necessary, by admitting a controlled amount of air to the coking zone. The flame from this supplemental burner is kept well away from the charge to avoid oxidation of the coke and hydration or carbonation of the lime. This can be done because of the limited amount of burning required and the relative shortness of the coking zone.

Heat out 5. Sensible heat of the coke-lime mixture discharged. The actual value will depend upon the coking temperature desired which is in turn determined by the requirements of the subsequent electric furnacing process.

6. Sensible heat in the gases leaving the coking zone. This will also depend on the coking temperature desired.

7. Radiation and convection losses. Because of the compactness of the apparatus, these will be small.

Obviously, heat input must equal heat output. Where a low coking temperature is desired for any reason, items 1 and 2 may provide all the heat necessary, and the supplemental burner can be eliminated. When a high coking temperature is required, supplemental heating is required to the extent necessary to achieve a heat balance. Such supplemental burning does not, however, detract in any way from the fundamentally high efficiency of the process. The supplemental burner does not use supplemental fuel unless supplemental fuel is required anyway for the reasons explained under paragraph 2. Further, the heat not transferred to the coking zone by radiation passes into the calcining zone where it is utilized.

The method as described has several important advantages. It requires no substantial complication of equipment over that normally required for lime burning. Heating of the coal is carried out in a substantial atmosphere of coal gas and in the absence of objectionable quantities of air or products of combustion. The coal heating zone is capable of being independently controlled with respect to temperature, agitation and retention time. These advantages are especially important in the preparation of mixtures or agglomerates containing carbonaceous fuel and lime or ore. In the event that the ratio of carbonaceous fuel to lime is low and sufficient heat cannot be obtained from the volatile products of the coal supplied, supplemental heating may be used as by supplying fuel with the air introduced through the pipe 20 which becomes a burner adapted to afford whatever heat may be necessary to maintain the required heat balance. The preparation of the material in the manner described materially facilitates subsequent treatment of the product in furnace operations.

Various changes may be made in the details of the procedure and in the apparatus employed without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method of continuously producing calcined material intimately mixed with carbonaceous fuel which comprises continuously advancing the material to be calcined through a heating and calcining zone extending from one end of a chamber to and through a coking and agglomerating zone at the other end of said chamber, calcining the material as it passes through the heating and calcining zone, adding a carbonaceous substance containing volatile combustible constituents to the advancing material after the calcination thereof is substantially complete and as it enters the coking and agglomerating zone, supplying heat to the carbonaceous substance while it is advancing through the coking and agglomerating zone with the calcined material in amount sufiicient to volatilize volatile constituents of the carbonaceous substance, admixing air with said volatilized constituents in amount suflicient to efiect combustion thereof but insuificient to effect complete burning of the residue resulting from the release of the volatile constituents, the admixing of the air with the volatile constituents being upstream of the travel of the material from where the carbonaceous substance is added to the calcined material, burning the resulting mixture of air and volatilized constituents and projecting the flame from such burning into the calcining zone to supply heat for said calcination of the material, and finally discharging the mixture of calcined material and residue of the carbonaceous substance from the coking and agglomerating zone.

2. The method of claim 1 in which the material to be calcined is limestone.

3. The method of claim 1 in which the material to be calcined is calcium hydrate sludge.

4. The method of claim 1 in which the material to be calcined is lime, the carbonaceous substance is coal and the residue resulting from the release of the volatile constituents from the coal is coke.

5. The method of claim 1 in which supplemental air is introduced into the coking and agglomerating zone downstream in the travel of the calcined material from where the carbonaceous substance is introduced.

6. A rotary kiln comprising a rotatable cylinder having a calcining zone and a coking and agglomerating zone, means for introducing material to be calcined into the kiln at one end thereof and into the calcining zone, a stationary hood extending about the end of the cylinder remote from the end where the material to be calcined is introduced, a pipe for the introduction of air into the cylinder extending through the hood and into the cylinder along approximately its central axis to a point substantially removed from the discharge end thereof, a conduit for introducing a carbonaceous material into the coking and agglomerating zone extending through said hood approximately parallel to the air feeding pipes and a substantial distance into the coking and agglomerating zone, the discharge end of said conduit terminating adjacent the discharge end of the air feeding pipe but spaced a short distance therefrom towards the discharge end of the cylinder.

7. A rotary kiln as set forth in claim 6 which also includes a pipe extending through the hood and into the cylinder for introducing supplemental air into the cylinder, said pipe having its discharge end terminating between the discharge end of the cylinder and the point of introduction of the carbonaceous material.

CHARLES J. McFARLIN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 894,507 King July 28, 1908 1,292,386 Becket Jan. 21, 1919 1,319,426 Slocum Oct. 21, 1919 1,810,070 Bunce June 16, 1931 1,830,002 Schifierle Nov. 3, 1931 1,866,203 Folliet et al. July 5, 1932 1,875,249 Mahler et al. Aug. 30, 1932 1,917,942 Kalling et al. July 11, 1933 2,116,030 Lindman May 3, 1938 2,222,585 Riggs Nov. 19, 1940 2,282,584 Hill May 12, 1942 2,298,257 Reaser et a1. Oct. 6, 1942 2,380,008 Abrams et al. July 10, 1945 2,414,625 Abrams et al. Jan. 21, 1947 2,429,416 Lesher Oct. 21, 1947 FOREIGN PATENTS Number Country Date 9,901 Great Britain 1911 22,236 Great Britain 1911 

1. THE METHOD OF CONTINUOUSLY PRODUCING CALCINED MATERIAL INTIMATELY MIXED WITH CARBONACEOUS FUEL WHICH COMPRISES CONTINUOUSLY ADVANCING THE MATERIAL TO BE CALCINED THROUGH A HEATING AND CALCINING ZONE EXTENDING FROM ONE END OF A CHAMER TO AND THROUGH A COKING AND AGGLOMERATING ZONE AT THE OTHER END OF SAID CHAMBER, CALCINING THE MATERIAL AS IT PASSES THROUGH THE HEATING AND CALCINING ZONE, ADDING A CARBONACEOUS SUBSTANCE CONTAINING VOLATILE COMBUSTILE CONSTITUENTS TO THE ADVANCING MATERIAL AFTER THE CALCIATION THEREOF IS SUSTANTIALLY COMPLETE AND AS IT ENTERS THE COKING AND AGGLOMERATING ZONE, SUPPLYING HEAT TO THE CARBONACEOUS SUBSTANCE WHILE IT ENTERS THE COKING AND THROUGH THE COKING AND AGGLOMERATING ZONE WITH THE CALCINED MATERIAL IN AMOUNT SUFFICIENT TO VOLATILIZE VOLATILE CONSTITUENTS OF THE CARBONACEOUS SUBSTANCE, ADMIXING AIR WITH SID VOLATILIZED CONSTITUENTS IN AMOUNT SUFFICIENT TO COMBUSTION THEREOF BT INSUFICIENT TO EFFECT COMPLETE BURNING OF THE RESIDUE RESULTING FROM THE RELEASE OF THE VOLTILE CONSTITUENTS, THE ADMIXING OF THE AIR WITH THE VOLATILE CONSTITUENTS BEING UPSTREAM OF THE TRAVEL OF THE MATERIAL FROM WHERE THE CARBONACEOUS SUBSTANCE IS ADDED TO THE CALCINED MATERIAL, BURNIG THE RESULTING MIXTURE OF AIR AND VOLATILIZED CONSTITUENTS AND PROJECTING THE FLAME FROM SUCH BURNING INTO THE CALCINING ZONE TO SUPPLY HEAT FOR SAID CALCINATION OF THE MATERIAL, AND FINALLY DISCHARGING THE MIXTURE OF CALCINED MATERIAL AND RESIDUE OF THE CARBONACEOUS SUBSTANCE FROM THE COKING AND AGGLOMERATING ZONE. 